This invention relates to a compressor, and more particularly, to a scroll type compressor for an air conditioning apparatus which includes a mechanism for adjusting the displacement of the compressor.
Scroll type fluid displacement apparatus are well known in the prior art. For example, U.S. Pat. No. 801,182 (Creux) discloses a device including two scrolls each having a circular end plate and a spiroidal or involute spiral element. These scrolls are maintained angularly and radially offset so that both spiral elements interfit to make a plurality of line contacts between their spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbital motion of the two scrolls shifts the line contacts along the spiral curved surfaces and, as a result, the volume of the fluid pockets changes. Since the volume of the fluid pockets increases or decreases dependent on the direction of the orbital motion, this scroll type fluid displacement apparatus is applicable to compress, expand or pump fluids.
Scroll type fluid displacement apparatus are suitable for use as refrigerant compressors in air conditioners. In such air conditioners, thermal control in the room or control of the air conditioner is generally accomplished by intermittent operation of the compressor. Once the temperature in the room has been cooled to a desired temperature, the refrigerant capacity of the air conditioner for supplemental cooling, because of further temperature changes in the room, or for keeping the room at the desired temperature, generally need not be very large. However, since prior art air conditioners do not have capacity control mechanisms, after the room has been cooled to the desired temperature, the output of the compressor is controlled by intermittent operation of the compressor. Thus, the relatively large load which is required to drive the compressor is intermittently applied to the driving source.
When prior art scroll compressors are used in automotive air conditioners, they are driven by the automobile engine through an electromagnetic clutch. Once the passenger compartment reaches a desired temperature, control of the output of the compressor is accomplished by intermittent operation of the compressor through the electromagnetic clutch. Thus, the relatively large load which is required to drive the compressor is intermittently applied to the automobile engine.
Therefore, it is desirable to provide a scroll compressor with a displacement or volume adjusting mechanism which controls the compression ratio as occasion demands. In a scroll type compressor, the adjustment of the displacement can be easily accomplished by controlling the volume of the sealed off fluid pockets. A displacement adjusting mechanism is disclosed in our co-pending application Ser. No. 356,648, filed on Mar. 9, 1982. This latter application discloses a mechanism including a pair of holes formed through one of the end plates of one of the scrolls. The holes are placed in symmetrical positions so that the wrap of the other scroll simultaneously crosses over the holes. In this compressor, the holes are placed within an area between .phi.end and .phi.end-2.pi., where .phi.end is the final involute angle of the wrap. Because of the location of these holes in the area between the end of the wrap and .phi.end-2.pi., part of the fluid in the sealed off fluid pockets leaks to the suction chamber through the holes. As a result, no compression takes place until the fluid pockets pass the hole at location defined .phi.end-2.pi.. However, when the holes are placed within the area between .phi.end and .phi.end-2.pi., the volume reduction ratio or capacity adjustment capability is limited.